Resistive-type Humidity Sensor Research Articles

Synthesis-in-place of V2O5 nanobelts for wide range humidity detection

Resistive type humidity sensors offer advantages in simplicity, low cost, compact size, and remote operation. Due to the benefits, they have great potential for use in a variety of environments and future applications, including the Internet of Everything (IoE). However, resistive humidity sensors have limitations in detecting extreme humidity levels below 10 % or above 90 % relative humidity (RH) and are also vulnerable to high temperatures, which hinders their use in harsh environments applications. For broader applications, humidity sensors with reliable performance across the full range of humidity levels and high stability at elevated temperatures need to be developed. Here, we report high performance resistive humidity sensors based on V2O5 nanobelts operating at high temperatures. The V2O5 nanobelts are directly deposited between Pt electrodes by O2-assisted physical vapor transport (PVT) method. The V2O5 nanobelt humidity sensor exhibits reliable humidity sensing properties over a wide range from 1 % to 100 % RH. Furthermore, long-term stability and reproducibility of V2O5 nanobelts are demonstrated through 25 consecutive humid air pulses and measurements obtained after 4 months of storage. The high performance of the V2O5 nanobelt humidity sensor is advantageous for practical use in applications ranging from IoE environments to harsh industrial conditions.

A comparative study on humidity response of graphene oxide with reduced graphene oxide and its multifunctional applications

In this paper, we present a comparative study of Graphene Oxide (GO) and chemically reduced Graphene Oxide (rGO) based resistive type humidity sensors fabricated on Ti/Au Inter-Digital Electrodes (IDEs) coated SiO2 substrates. The sensing performance, including sensitivity, response/recovery time, and hysteresis has been evaluated for both sensors. The GO film exhibited quick response (0.3 s) and high sensitivity (104.7 kΩ/%RH) with remarkable repeatability and negligible hysteresis as compared to rGO film sensor. The excellent humidity sensing properties of GO are attributed to the presence of abundant oxygen-containing polar functional groups on GO relative to rGO. To demonstrate the multifunctional applications of developed GO based sensor, we have also demonstrated its use as respiratory monitoring, non-contact proximity detector, and speech event detector through the detection of humidity perturbations. The work suggests GO sensitive material has high potential for the development of wearable and integrated health monitoring platforms and non-contact sensing devices.

Biosynthesis, structural characterization and humidity sensing properties of cellulose/ZnO nanocomposite

The present work demonstrates the applications of a nanocomposite of the cellulose polymer and ZnO nanoparticles with 1:1 weight ratio, prepared by a green assisted precipitation method for a high-performance resistive type humidity sensor. The morphology and nanostructure of prepared cellulose/ZnO composite were characterization by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy and transmission electron microscopy are confirmed the decoration of ZnO nanoparticles on cellulose polymer matrix surface. The humidity sensing martials was coated onto the interdigital electrodes. The sensitivity, response/recover and stability studies performance of fabricated humidity sensors have been monitored in 5 to 98% relative humidity (%RH) at room temperature (37 °C). The response and recovery times of the fabricated sensors are observed as ≈ 26 s and ≈ 53 s respectively, and the sensitivity factor (Sf) is 2656 ± 103 Ω. Possible mechanisms of the humidity sensor based on water-induced conductivity increase are discussed. Also, the energy band of cellulose/ZnO nanocomposite was simulated by density functional theory (DFT) studies. The cellulose/ZnO nanocomposite humidity sensor has great potential for practical field applications.

Influence of Anodic Aluminum Oxide Nanostructures on Resistive Humidity Sensing

Humidity nanosensors play a vital role in modern technology industries, including weather forecasts, industrial manufacturing, agriculture, food and chemistry storage. In recent years, research on humidity sensors has focused on different materials such as ceramics, polymers, carbon-based materials, semiconductors, MXenes or triboelectric nanogenerators, each with their own advantages and disadvantages. Among them, anodic aluminum oxide (AAO) is a well-known ceramic humidity sensor material with a long history of research and development. AAO humidity sensors offer advantages such as simple manufacturing processes, controllable nanostructures, high thermal stability and biocompatibility. However, traditional AAO fabrication still has disadvantages like high costs and longer process times. Hence, finding a low-cost and efficient method to fabricate AAO for controlling different nanostructures to meet the requirements is consistently a major research topic. From our previous studies, we have studied the relationship between the AAO capacitive humidity sensor and its nanostructures. In this paper, we explore the effect of an AAO nanoporous structure controlled by an anodization voltage of 20–40 V on the resistive-type humidity sensor performance instead of a capacitive one. We efficiently apply one-step hybrid pulse anodization at 25 °C to significantly reduce the processing time compared to the traditional two-step process under 0–10 °C. The AAO nanostructures and their impact on sensor measurements of humidity at 20–80 RH% will be discussed in detail. An electrical resistive sensing mechanism is established for further performance improvement by controlling anodization voltage.

Graphene oxide boosted high surface area CeO2 for humidity sensing

Precise measurement of humidity is of high significance in diverse fields like instrumentation, automated systems, agriculture and climatology. Herein as a first ever attempt, we report ceria-graphene oxide (CeO2-GO) composites as resistive type humidity sensor, that shows attractive response to moisture. High surface area ceria is synthesised via ammonia mediated precipitation from salt precursor, and CeO2-GO composites are achieved via hydrothermal route. The composites are well characterized using various analytical tools. Experiments using different mass ratios of GO in the composite show that there is an optimum amount of GO to realise maximum efficiency in the test parameters. It is further noted that the performance of the sensor is controlled by the active adsorption sites, which is proportional to surface area of the composite. An optimized CeO2-GO matrix yielded a response and recovery time of 19 s and 10 s respectively. The narrow hysteresis in moisture adsorption-desorption study and excellent stability for about 60 days are also observed for the system, warranting the successful utility of the system for practical applications.

A high-performance humidity sensor based on 3D porous SnO2-encapsulated MCM-48 for real-time breath monitoring and contactless gesture detection

Ordered porous SnO2/MCM-48 was used as a basis for developing a resistive-type humidity sensor was demonstrated for real-time respiration monitoring and no-contact sensing for the first time.

Chitosan-Based Highly Sensitive Viable Humidity Sensor for Human Health Monitoring.

We report a sustainable resistive-type humidity sensor based on chitosan (CS) film deposited on an interdigitated Ti/Au electrode coated SiO2 substrate using a simple drop cast approach for human health monitoring. The sensor revealed remarkably high sensitivity (5.8 MΩ/%RH), fast response/recovery time (21 s/25 s), low hysteresis (∼9.3%), excellent reversibility, wide detecting range (11-95% RH), and high selectivity toward water vapor. The calculated associated uncertainty at different %RH indicates the excellent repeatability and stable performance of the sensor. The developed sensor is tested for different human breath patterns, and it is found that the sensor can clearly distinguish between the variations in rate and depth of respiration patterns during normal, fast, deep, and nasal breathing and can monitor for apnea-like situations. The sensor is also utilized to perform noncontact skin humidity sensing. Overall, the developed CS film humidity sensor provides a viable approach for the detection of respiratory disorders and human health issues, detected by skin moisture, in a noninvasive manner.

Use of highly sensitive nickel phthalocyanine based humidity sensor to explore the imprecise data analysis for robot body

PurposeThe purpose of this study is to fabricate a highly sensitive humidity sensor for observing the humidity effect on a robot’s body as an application of the Internet of Things. The sensor has been fabricated by depositing a thin sensing layer of nickel phthalocyanine (NiPc) between two silver electrodes.Design/methodology/approachThe structure of the thin film was observed by X-ray diffraction, optical properties by UV Vis and surface morphology by scanning electron microscope. The capacitance and the resistance with respect to change in relative humidity from 0 to 100%RH have been measured by LCR meter at 1 kHz.FindingsThe sensor’s response time is 7.5 s and its recovery time is 3.7 s, with high sensitivity of 127,259 pF/%RH and 332.287 MΩ/%RH. The authors have also used a proposed sensor on a steel body and observed humidity values. The analysis of all measured values was performed through the classical and neutrosophic approaches. By comparing, the authors have observed that the neutrosophic approach is more efficient in analyzing the sensor data.Originality/valueIn this work, the authors will fabricate a capacitive and resistive-type humidity sensor using the thin film of NiPc. The structural, optical and morphological properties of NiPc thin film will be investigated with different characterization techniques. The electric properties, i.e. capacitance and resistance, will be measured at intervals with an LCR meter by changing relative humidity (%RH). Moreover, the measured data will be analyzed through different statistical approaches, as already used in [12].

An All-Printed, Fast-Response Flexible Humidity Sensor Based on Hexagonal-WO3 Nanowires for Multifunctional Applications.

The utilization of printing techniques for the development of high-performance humidity sensors holds immense significance for various applications in the fields of the Internet of Things, agriculture, human healthcare, and storage environments. However, the long response time and low sensitivity of current printed humidity sensors limit their practical applications. Herein, a series of high-sensing-performance flexible resistive-type humidity sensors is fabricated by the screen-printing method, and hexagonal tungsten oxide (h-WO3 ) is employed as the humidity-sensing material due to its low cost, strong chemical adsorption ability, and excellent humidity-sensing ability. The as-prepared printed sensors exhibit high sensitivity, good repeatability, outstanding flexibility, low hysteresis, and fast response (1.5s) in a wide relative humidity (RH) range (11-95%RH). Furthermore, the sensitivity of humidity sensors can be easily adjusted by altering the manufacturing parameters of the sensing layer and interdigital electrode to meet the diverse requirements of specific applications. The printed flexible humidity sensors possess immense potential in various applications, including wearable devices, non-contact measurements, and packaging opening state monitoring.

SnO2 nanostructured thin film as humidity sensor and its application in breath monitoring

In the present paper, we studied SnO2 nanostructured thin film-based resistive type humidity sensor fabricated by spin coating method on alumina substrate and showed its application in real time respiratory monitoring. Experiments show the growth of crystalline SnO2 nanoparticles with a tetragonal phase, with an average particle size of ∼15 nm and a high surface roughness of the order of 50-60 nm. The gold-interdigitated electrodes were patterned on the SnO2 film surface by DC sputtering technique to study the sensing response of the film. The sensor shows a high sensitivity of 1.34 kΩ/%RH, a minimal hysteresis of 0.94%, and good repeatability. The developed sensor is tested for monitoring human breath patterns in different physical conditions, and apnea like situations, which suggests its potential for clinical applications. Overall, the present work proposes an environmental friendly, easy-to-synthesize, highly stable, and simple facile SnO2 based deployable humidity sensor to diagnose human health patterns in a non-contact manner.

Geometric design optimization of polyaniline/graphite nanocomposite based flexible humidity sensor for contactless sensing and breath monitoring

• Polyaniline-graphite nanocomposite based 2D humidity sensor was screen-printed. • Adding graphite leads to faster response, improved thermal stability and hysteresis. • Improved long term stability with high performance was demonstrated over 180 days. • Sensor geometry (inter-electrode distance and number of electrodes) was optimized. • Contactless sensing and respiration monitoring applications were demonstrated. We report a low cost flexible polyaniline-graphite nanocomposite based resistive type humidity sensor, screen printed on a PET substrate with interdigitated silver electrodes. The composite with a 3:1 ratio of polyaniline and graphite was found to be ideal with a sensing response of 93.4%, took 24 s to reach 54% RH, a maximum response/recovery time of 35/39 s and low hysteresis (1.12%). Graphite acting as the support material increased the sensor's thermal stability, allowing it to be operated at temperatures as high as 55 ⁰C. To further improve sensor performance and find an optimum device architecture, geometric parameters such as inter-electrode distance and number of electrodes were studied and optimised. Based on this, a relative humidity contactless finger sensor (1.5 cm range) and a human breath monitoring sensor to map different breathing rates were demonstrated.

Composite Effect on Zinc Oxide based Resistive Type Humidity Sensor Performance: A Preliminary Assessment

Composite Effect on Zinc Oxide based Resistive Type Humidity Sensor Performance: A Preliminary Assessment

Direct ink write printing of resistive-type humidity sensors

To practice the development of printed electronics, researchers need to have the access to dedicated printer of electronic materials. However, commercial printing machines require large capital investment. Direct ink write (DIW) printing on the other hand operates with single printing head and less complex system therefore is promising for tight budget projects. Herein, a DIW printing system was home-built by making modifications to a 3D printer with ready to use components. Direct pattering and minimal printing line width of 230 ± 10 µm are demonstrated using an all solution-based Ag ink. Resistive-type humidity sensors were fabricated with DIW printed Ag electrodes and poly (diallyl dimethyl ammonium chloride) (PDDA) sensing layer. Humidity sensing performance of the sensors were examined and by taking advantage the flexibility of printing deposition, DIW printing was used to make quick modification toward a partially covered sensor structure for improved performance. Sensing response of more than 99% was obtained from 10% RH to 90% RH. Smaller hysteresis of ±4.4% RH and faster response of 7 s for adsorption and 213 s for desorption were obtained with the partially covered sensor. DIW printing is found to be a useful tool for device prototyping and ink development of printed electronics.

Nitrogen-doped carbon oxide quantum dots for flexible humidity sensor: Experimental and SCC-DFTB study

A flexible resistive-type humidity sensor based on N-type nitrogen-doped carbon oxide quantum dots (NCQDs) is presented. The NCQDs were synthesized by using simple hydrothermal method with reactions via citric acid and urea. The UV–vis, FE-TEM and XPS analysis confirm a successful doping of N atoms and existence of oxygen-containing functional groups into carbon quantum dots with the homogeneous spherical structure. The NCQDs humidity sensor exhibits high humidity response, good repeatability, and high stability as well as linear response to humidity in the range of 20–90% RH. The humidity sensing mechanism has been in-depth investigated by self-consistent charge density functional tight-binding (SCC-DFTB) including dispersion interaction. The SCC-DFTB reveals an important role of N doping with physisorption via direct charge transfer sensing mechanism.

High-performance resistive humidity sensor based on Ag nanoparticles decorated with graphene quantum dots.

In this work, we present a low-cost, fast and simple fabrication of resistive-type humidity sensors based on the graphene quantum dots (GQDs) and silver nanoparticles (AgNPs) nanocomposites. The GQDs and AgNPs were synthesized by hydrothermal method and green reducing agent route, respectively. UV–Vis spectrophotometer, X-ray photoelectron spectroscopy and field-emission transmission electron microscopy were used to characterize quality, chemical bonding states and morphology of the nanocomposite materials and confirm the successful formation of core/shell-like AgNPs/GQDs structure. According to sensing humidity results, the ratio of GQDs/AgNPs 1 : 1 nanocomposite exhibits the best humidity response of 98.14% with exponential relation in the humidity range of 25–95% relative humidity at room temperature as well as faster response/recovery times than commercial one at the same condition. The sensing mechanism of the high-performance GQDs/AgNPs humidity sensor is proposed via Schottky junction formation and intrinsic synergistic effects of GQDs and AgNPs.

Synthesis and characterization of natural zeolite-clay as resistive humidity detection

Zeolite-clay was successfully employed in as resistance type humidity sensor. Zeolite-clay humidity sensor was synthesized by crushing into powder and soaked into 6% H2SO4while stirred for two hours using a magnetic stirrer. The solution was filtered, washed using aquadest and dried at 100°C for 5 hours with the mixture process of zeolite and clay were varied into 10%:0%, 9.5%:0.5%, 9%:1%, 8.5%:1.5%, and 8%:2%. The result pressed with a size of 3x3x1 cm3 using a hydraulic under 3 tons pressure for 10 minutes and heated at temperatures of 800°C.Zeolite-clay was placed in a testing chamber equipped with the electrode that connected to an electrical supply of 3 Volt. The electrical resistance was recorded using Multimeter Hydra Series III Fluke when exposed with humidity in range of 18.5-99% RH. Zeolite 8%-clay 2% sensor exhibits the highest sensitivity properties, which indicate saturated resistance value at 99% RH.Meanwhile, Zeolite 8.5 gr-clay 1.5 gr revealed the highest response value at 54.3 Mega Ohm. Based on SEM and EDX characterization, the ratio of Si/Al and microstructure surface have an effect towards humidity detection process. The results indicate enhancement than previous research on zeolite as a sensor, and therefore Zeolite-Clay has proved the capability to detect humidity.

Humidity Sensing Performance of V: TiO2 3D Nanostructure-based Humidity Sensor

Titanium dioxide (TiO2) three-dimensional (3D) nanostructure has been prepared and doped with vanadium (V) using a solution immersion method. The resultant material exhibited improved performance in the role of the sensing element in resistive-type humidity sensor. The improvement is attributed to the arrangement of the nanorod structure which appears to be more closely packed in the V-doped TiO2 when compared to the undoped TiO2. Another possible reason is due to the increased of defect sites, namely oxygen vacancies of the V-doped sample which enhance the dissociation of the adsorbed water molecules.

Ultrasensitive and reversible room-temperature resistive humidity sensor based on layered two-dimensional titanium carbide

The nanostructured two-dimensional (2D) materials for humidity sensing applications have become increasingly attractive. However, 2D materials have negative aspects of easily stacking and agglomerating multilayers. Here, a novel resistive-type humidity sensor utilizing multi-layer titanium carbide (Ti3C2Tx) films as sensitive material is demonstrated. The humidity sensor exhibits an ultrasensitive and reversible sensing performance in a wide relative humidity range. Furthermore, the ultrafast response and recovery properties are achieved at room temperature. The Fourier transform infrared spectroscopy is used to investigate the adsorption of water vapor on Ti3C2Tx surfaces. A rapid capillary condensation of water vapor on the unique accordion-like microstructures and the hierarchical nanostructures of hydroxyl-riched Ti3C2Tx surface are supposed to be responsible for the super adsorption capability for water vapor. The electrostatic field induced by adsorbed water molecules is proposed to explain the resistance change of the titanium carbide humidity sensor. This work highlights the unique advantages of humidity sensor with layered 2D materials of Ti3C2Tx MXenes, including ultrasensitive, good reversibility and fast recovery at room temperature.

The efficacy of polyvinylpyrrolidone (PVP)/CuO nanocomposite as an appropriate room temperature humidity sensing material: fabrication of highly sensitive capacitive resistive type humidity sensor

The efficacy of polyvinylpyrrolidone (PVP)/CuO nanocomposite as an appropriate room temperature humidity sensing material: fabrication of highly sensitive capacitive resistive type humidity sensor

Comparative Study of Structural, Morphological and Humidity Sensing Properties of Pure WO3 and Cu2O-WO3 Nanocomposite

This work reports the enhancement of humidity sensing properties of tungsten trioxide (WO3) by the formation of nanocomposite with cuprous oxide (Cu2O). A 0.1 g of Cu2O was mixed with 0.9 g of WO3. Pellets of pure WO3 and the obtained mixture are prepared at pressure of 250 MPa applied for 0.5 h. The pellets were then annealed at 300 ºC, 400 ºC, 500 ºC and 600 ºC. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyzed the crystallinity and morphology of as-prepared pellets surface. Humidity sensing application of pellets is studied in a specially designed chamber. It is observed that as relative humidity increases, there is decrease in the resistance of the pellets. The humidity-sensing investigation (10-99%RH) showed that the nanocomposite of Cu2O with WO3 annealed at 600 ºC, is having the best sensitivity, low hysteresis, less ageing and high reproducibility than pure WO3. It is also observed that as annealing temperature increases from 300 to 600 ºC, sensitivity increases. The present investigation could be useful for fabrication of resistive type humidity sensors for commercial applications.